Platinum(0)-catalyzed intramolecular addition of a C-H bond onto the P=C bond of a phosphaalkene

Article abstract of DOI:10.1021/om9006664

The phosphaalkene E-Mes*P=CHPh (1) reacts with a stoichiometric amount of [Ni(COD)₂] at room temperature for 15 h in hexanes to afford the 1-P-benzyl-benzophospholane 2, which results from the formal addition of the C-H bond of one tert-butyl g

Full text of DOI:10.1021/om9006664

5952 Organometallics 2009, 28, 5952–5959
DOI: 10.1021/om9006664
Platinum(0)-Catalyzed Intramolecular Addition of a C-H Bond onto the
PdC Bond of a Phosphaalkene
ꢀ
Romaric Houdard, Nicolas Mezailles, Xavier-Frederic Le Goff, and Pascal Le Floch*
ꢀ ꢀ ꢀ ꢀ
Laboratoire “Heteroelements et Coordination”, Ecole Polytechnique, CNRS, 91128 Palaiseau Cedex,
France
Received July 28, 2009
The phosphaalkene E-Mes*PdCHPh (1) reacts with a stoichiometric amount of [Ni(COD)2] at
room temperature for 15 h in hexanes to afford the 1-P-benzyl-benzophospholane 2, which results
from the formal addition of the C-H bond of one tert-butyl group onto the PdC double bond. The
formulation of benzophospholane 2 was confirmed by an X-ray diffraction study of the correspond-
ing trans [Pd(2)Cl2] complex 3a (meso complex). Formation of 2 was also achieved by using a catalytic
amount of the [Pt(PCy3)2] catalyst (20 mol %) in hexanes at 65 °C for 15 h. Extension of this
procedure to the bis-phosphaalkene [(E)-Mes*PdCH]2-(m-C6H4) (4) afforded the corresponding bis-
benzophospholane, which was recovered as a mixture of diastereomers 5a and 5b. On the basis of
DFT calculations a complete mechanistic pathway was proposed in the case of nickel. The overall
mechanism involves a preliminary complexation of 1 at Ni to afford a 12 VE Z1-complex, which then
evolves to yield the 14 VE Z2-species featuring coordination of one C-H of a tert-butyl group.
Insertion of nickel into this C-H bond followed by the formation of a P-C bond between
phosphorus and the methyl group affords a 14-VE hydrido complex featuring a Z3-benzyl ligand.
Isomerization of this species through complexation of the phosphorus atom of the benzophos-
pholane unit and decomplexation of the phenyl group affords a 14-VE species, which undergoes a
reductive elimination to finally yield the 12-VE Ni complex of 2. A similar mechanism was proposed
in the case of platinum considering that the catalytically active species is the 12-VE [Pt(PMe3)]
complex. In good agreement with NMR data this mechanism involves, as the most stable inter-
mediate, a 16-VE complex featuring the benzophospholane ligand, which is coordinated to the
[Pt(H)(PMe3)] fragment through the phosphorus atom lone pair and the benzylic carbon atom. NMR
data and DFT calculations confirm that, in this intermediate, the hydride is located trans to the
phosphorus atom of the benzophospholane ligand.
Introduction
important synthetic value.3 In addition, the presence of both
a polarized σ-system and a genuine π-system makes them
interesting and versatile precursors of acyclic and cyclic
Phosphaalkenes, the phosphorus equivalents of alkenes
and imines, constitute a very peculiar class of compounds.1
Thanks to their electronic properties, which profoundly
differ from that of their nitrogen counterparts, they have
found numerous applications in coordination chemistry, for
example, in the stabilization of very electron rich metal
fragments.2 They also found important applications as
ligands in homogeneous catalysis in transformations of
(3) See for example: (a) Minami, T.; Okamoto, H.; Ikeda, S.; Tanaka,
R.; Ozawa, F.; Yoshifuji, M. Angew. Chem., Int. Ed. 2001, 40, 4501. (b)
Ozawa, F.; Okamoto, H.; Kawagishi, S.; Yamamoto, S.; Minami, T.;
Yoshifuji, M. J. Am. Chem. Soc. 2002, 124, 10968. (c) Daugulis, A.;
Brookhart, M.; White, P. S. Organometallics 2002, 21, 5935. (d) Ionkin,
A.; Marshall, W. Chem. Commun. 2003, 710. (e) Ozawa, F.; Ishiyama, T.;
Yamamoto, S.; Kawagishi, S.; Murakami, H.; Yoshifuji, M. Organometallics
2004, 23, 1698. (f) Murakami, H.; Minami, T.; Ozawa, F. J. Org. Chem.
2004, 69, 4482. (g) Murakami, H.; Matsui, Y.; Ozawa, F.; Yoshifuji, M.
J. Organomet. Chem. 2006, 691, 3151. (h) Katayama, H.; Nagao, M.;
Nishimura, T.; Matsui, Y.; Umeda, K.; Akamatsu, K.; Tsuruoka, T.;
Nawafune, H.; Ozawa, F. J. Am. Chem. Soc. 2005, 127, 4350. (i) Nagao,
M.; Asano, K.; Umeda, K.; Katayama, H.; Ozawa, F. J. Org. Chem. 2005, 70,
10511. (j) Katayama, H.; Nagao, M.; Nishimura, T.; Matsui, Y.; Umeda, K.;
Akamatsu, K.; Tsuruoka, T.; Nawafune, H.; Ozawa, F. J. Am. Chem. Soc.
2005, 127, 4350. (k) Nagao, M.; Asano, K.; Umeda, K.; Katayama, H.;
Ozawa, F. J. Org. Chem. 2005, 70, 10511. (l) Hayashi, A.; Okazaki, M.;
Ozawa, F. Organometallics 2007, 26, 5246. (m) Deschamps, B.; Le Goff,
X.-F.; Ricard, L. Heteroat. Chem. 2007, 18, 363. (n) Dugal-Tessier, J.; Dake,
G. R.; Gates, D. P. Organometallics 2007, 26, 6481. (o) Hayashi, A.;
Yoshitomi, T.; Umeda, K.; Okazaki, M.; Ozawa, F. Organometallics 2008,
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Ed. 2008, 47, 8064. (q) Takita, R.; Takada, Y.; Jensen, R. S.; Okazaki, M.;
Ozawa, F. Organometallics 2008, 27, 6279.
*Corresponding author. E-mail: lefloch@polytechnique.fr.
(1) (a) Dillon, K. B.; Mathey, F.; Nixon, J. F. Phosphorus: The
Carbon Copy; Wiley: Chichester, 1998. (b) Le Floch, P. Coord. Chem.
Rev. 2006, 250, 627. (c) Mathey, F. Angew. Chem., Int. Ed. 2003, 42, 1578.
(d) Weber, L. Angew. Chem., Int. Ed. 2002, 41, 563. (e) Ozawa, F.; Yoshifuji,
M. C. R. Chim. 2004, 7, 747. (f) Ozawa, F.; Yoshifuji, M. Dalton Trans.
2006, 4987. (g) Yoshifuji, M. Pure Appl. Chem. 2005, 77, 2011.
(2) See for example: (a) Jouaiti, A.; Geoffroy, M.; Terron, G.;
Bernardinelli, G. J. Am. Chem. Soc. 1995, 117, 2251. (b) Tirla, C.;
Mezailles, N.; Ricard, L.; Mathey, F.; Le Floch, P. Inorg. Chem. 2002, 41,
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Chem. Commun. 2003, 1914. (d) Deschamps, E.; Deschamps, B.; Dormieux,
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ꢀ
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pubs.acs.org/Organometallics
Published on Web 10/02/2009
2009 American Chemical Society

Article
Organometallics, Vol. 28, No. 20, 2009 5953
tertiary phosphines through reactions with the PdC double
bond (additions of nucleophiles at phosphorus, epoxidation,
cycloadditions).1 More recently, they were also employed as
precursors of phosphorus polymeric materials through ra-
dical and anionic polymerization and copolymerization
processes.4 An interesting parallel can therefore be drawn
between the reactivity of phosphaalkenes and that of al-
kenes. The challenge consisting in duplicating the chemistry
of alkenes to phosphaalkenes still remains of utmost impor-
tance. As part of a study on the reactivity of kinetically
stabilized phosphaalkenes toward zerovalent group 10 com-
plexes, we recently found that intramolecular addition of a
C-H bond onto a PdC double bond could be stoichiomet-
rically and catalytically promoted by Ni(0) and Pt(0) com-
plexes, respectively. Herein we report on these experimental
finding as well as on a complete theoretical DFT study that
allows us to propose a rational mechanism in both cases.
Figure 1. Molecular structure of complex 3a with thermal
ellipsoids projected at the 50% probability level. The numbering
is arbitrary and different from that used in the 13C NMR
˚
Results and Discussion
spectrum. Selected bond distances (A) and angles (deg): Pd-P-
(1) 2.3345(7), P(1)-C(1) 1.833(2), P(1)-C(8) 1.835(2), Pd-P(10)
2.3345(7), Pd-(Cl1) 2.3109(6), P(1)-Pd-Cl(1) 86.48(2), P-
(1)-Pd-P(10) 180.0, Pd-P(1)-C(1) 110.6(1), Pd-P(1)-C(8)
116.8(1), C(1)-P(1)-C(8) 94.2(1).
Unlike what we had initially expected, reacting E-Mes*-
PdCHPh (Mes* = 2,4,6-tri-tert-butylphenyl) (1) with [Ni(CO-
D)2] in a 1 to 1 ratio in hexanes (mixture of isomers) at room
temperature did not afford a Ni(0) complex of 1. Indeed,
monitoring the reaction by 31P NMR spectroscopy revealed
the formation of a single new phosphorus derivative, 2, which
appears as a singlet at much higher field (δ = -7.2 ppm) than
1 (δ = 259 ppm). The formation of compound 2 was also
accompanied by deposition of metallic nickel (eq 1).
not be separated during the workup, but single crystals of
complex 3a, which is the meso-complex, were obtained by
slowly cooling a solution of the mixture of the two complexes
1
in hexanes at -25 °C. According to the H and 13C NMR
data of 3a and 3b, which are very similar, we can reasonably
assume that complex 3b also adopts a trans geometry.
Compound 2, which was found to be oxygen sensitive, was
obtained as a pale yellow solid after usual workup with a
60% yield. The formulation of 2, a 1-P-benzyl benzophos-
pholane, was established on the basis on 1H and 13C NMR
and mass spectrometry, as well as elemental data. In parti-
cular, two new signals, each integrating for one hydrogen
atom, are observed for the two diastereotopic benzylic
hydrogens at 3.00 and 2.61 ppm. They each appear as a
doublet of doublets resulting from the coupling with the
A view of one molecule of 3a is presented in Figure 1, and
the most significant metric parameters are listed in the
corresponding legend. Crystal data of complex 3a are re-
ported in Table 1. As can be seen, 1 is a very bulky ligand,
which probably does not favor the formation of a cis-[PdCl2]
complex. Apart from this, the structure of 3a does not
deserve further comment.
Further experiments were carried out to evidence the forma-
tion of intermediates in the formation of 2, but, whatever the
experimental conditions used, the 31P NMR spectrum of the
crude reaction mixture revealed only the presence of compounds
1 and 2. The use of catalytic conditions (20% of Ni(COD)2) did
not allow a full conversion to be reached, and the reaction
stopped very rapidly, with a concomitant precipitation of
metallic Ni. Addition of PCy3 as a stabilizing ligand of nickel
to form a soluble, and hopefully more stable, Ni(0) complex was
also attempted (5% Ni(COD)2 and 10% PCy3), but it did not
yield further improvement. Finally, the transformation with a
stoichiometric amount of Ni nanoparticles stabilized by TOP
(tri-n-octylphosphine) was also attempted, but no conversion
was observed.5
2
adjacent P atom (2JP-H = 6.3 Hz and JP-H = 6.0 Hz,
respectively) and with each other (2JH-H =13.3 Hz). This
was further confirmed by an X-ray crystal structure study of
its PdCl2 complex. Indeed, reaction of 2 with half an
equivalent of [Pd(COD)Cl2] in toluene at 110 °C overnight
cleanly afforded diastereomeric complexes 3a,b, which were
formed in a 3 to 2 ratio, respectively, and isolated with a
combined 92% yield (eq 2). Unfortunately, 3a and 3b could
(4) (a) Wright, V. A.; Gates, D. P. Angew. Chem., Int. Ed. 2002, 41,
2389. (b) Gates, D. P.; Tsang, C.-W.; Wright, V. A.; Yam, M. Macromol.
Symp. 2003, 196, 271. (c) Tsang, C.-W.; Yam, M.; Gates, D. P. J. Am. Chem.
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Gates, D. P. Angew. Chem., Int. Ed. 2004, 43, 5682. (e) Gillon, B. H.; Gates,
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7271. (h) Wright, V. A.; Patrick, B. O.; Schneider, C.; Gates, D. P. J. Am.
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Kingsley, J. J.; Yam, M.; Gates, D. P. Dalton Trans. 2008, 4451. (l) Noonan,
K. J. T.; Gates, D. P. Macromolecules 2008, 41, 1961. (m) Noonan, K. J. T.;
Gillon, B. H.; Cappello, V.; Gates, D. P. J. Am. Chem. Soc. 2008, 130,
12876.
(5) (a) Chen, Y. Z.; Peng, D. L.; Lin, D. P.; Luo, X. H. Nanotechnol-
ogy 2007, 18, 505703. (b) Park, J.; Kang, E.; Son, Su.; Park, H. M.; Lee,
M. K.; Kim, J.; Kim, K. W.; Noh, H. J.; Park, J. H.; Bae, C. J.; Park, J. G.;
Hyeon, T. Adv. Mater. 2005, 17, 429.

5954 Organometallics, Vol. 28, No. 20, 2009
Houdard et al.
Table 1. Crystallographic Data for Complex 3a
Scheme 1. Formation of a Benzophospholane from Mes*PdCH2
Catalyzed by AlCl3
empirical formula
mol wt
cryst habit
cryst size (mm)
cryst syst
space group
C50H70Cl2P2Pd(CH2Cl2)
1080.15
yellow block
0.24 ꢀ 0.24 ꢀ 0.22
orthorhombic
Pbca
˚
a (A)
16.311(1)
17.109(1)
19.404(1)
5415.0(5)
˚
b (A)
˚
c (A)
3
V (A )
˚
Z
4
1.325
0.731
30.03
2256
calcd density (g cm-3
)
abs coeff (cm-1
2Fmax (deg)
F(000)
)
the bis-benzophospholane 5 as a mixture of diastereomers in
a 1:1 ratio with a 82% yield. Compound 5 was recovered as a
white oxygen-sensitive solid after usual workup and identi-
fied by conventional NMR methods, mass spectrometry,
and elemental analysis (eq 4).
index ranges
-7 to 22; -23 to 16; -26 to 18
15 758/7427
3971
0.0326
multiscan; 0.8441 min, 0.8558 max
285
13
0.0444/0.1207
no. of collected/indep reflns
no. of reflns used
Rint
abs corr
no. of params refined
no. of reflns/param
final R1a/wR2b (I > 2σI)
goodness of fit on F2
0.918
1.043(0.079)/-0.481(0.079)
-3
˚
diff peak/hole (e A
)
P
P
P
P
a R1 =
Fo| - |Fc
/
|Fo|. b wR2 = ( w Fo| - |Fc
w|Fo|2)1/2
.
2
/
With the aim of developing a catalytic version of this
rearrangement, further experiments were also conducted
with the heavier congeners of the group 10 metals. In first
attempts, palladium was tested in the form of the [Pd(dba)2]
complex. The use of 20 mol % of catalyst at 65 °C for 20 h
yielded a conversion of only 5%. The use of PCy3 as a
stabilizing ligand of palladium (1 equiv with regard to the
catalyst) yielded the same conversion. Finally, the most
satisfying results were obtained by replacing nickel by plati-
num. Indeed, reaction of 1 with 10 mol % of the 14-VE
[Pt(PCy3)2] complex at 65 °C for 60 h in hexanes cleanly
afforded 2 with a 80% yield (eq 3). A similar conversion was
obtained with 20 mol % of catalyst after heating at 65 °C for
15 h.
Mechanism of the H Migration. The formation of benzo-
phospholane 2 results from the transfer of one hydrogen
atom of one tert-butyl group to the C-carbon atom of the
phosphaalkene. This type of rearrangement is not totally
unprecedented since Gates et al. reported on the reactivity of
Mes*PdCH2 toward MX3 (M = Al, Ga) in 2002.7 Interest-
ingly, they showed that, under catalytic conditions, an
intramolecular C-H activation took place to afford the
corresponding 1-P-methyl benzophospholane. On the basis
of isotopic labeling experiments, they proposed a convincing
mechanism relying on the transient formation of a phosphe-
nium species that further inserts into the C-H bond of a tert-
butyl group to form a P-H bond, followed by H migration
on the neighboring methylene fragment. The mechanism
proposed is depicted in Scheme 1.
Formation of 2 cannot be rationalized following a similar
pathway since under the conditions used no cationic species
are expected to be formed upon reacting [Ni(COD)2] or
[Pt(PCy3)2] with 1. In order to shed some light on our
transformation, DFT calculations were carried out in the
case of both nickel and platinum (see Experimental Section
for further details). In this study we did not consider the
complete substitution scheme of the Mes* group. Indeed, as
the para tert-butyl group is not expected to play a significant
role in the transformation, it was replaced by a H atom.
Mechanism with Ni. In the case of nickel, examination of
the 1H NMR data of the crude reaction mixture revealed that
the COD ligand is released during the process. As mentioned
½PtðPCy3Þ2ð10 mol %Þ
1
2
ð3Þ
f
hexanes, 65 °C, 60 h
Having found an efficient catalytic formation of benzo-
phospholane 2 from phosphaalkene 1, we wished to extend
this procedure to the formation of the corresponding bis-
benzophospholane, a potential precursor of a PCP pincer
ligand.6 Toward this goal, the bis-phosphaalkene 4 was
synthesized. Reaction of 4 with 20 mol % of the [Pt-
(PCy3)2] catalyst at 65 °C in hexanes for 15 h cleanly afforded
(6) Representative examples of PCP pincers systems: (a) Dani, P.;
Karlen, T.; Gossage, R. A.; Gladiali, S.; Van Koten, G. Angew. Chem.,
Int. Ed. 2000, 39, 743. (b) Albrecht, M.; Dani, P.; Lutz, M.; Spek, A. L.; Van
Koten, G. J. Am. Chem. Soc. 2000, 122, 11822. (c) Dani, P.; Albrecht, M.;
Van Klink, G. P. M.; Van Koten, G. Organometallics 2000, 19, 4468. (d)
Beletskaya, I. P.; Chuchuryakin, A. V.; Van Koten, G.; Dijkstra, H. P.; Van
Klink, G. P. M.; Kashin, A. N.; Nefedov, S. E.; Eremenko, I. L. Russ. J. Org.
Chem. 2003, 39, 1268. (e) Dijksra, H. P.; Albrecht, M.; Medici, S.; Van Klink,
G. P. M.; Van Koten, G. Adv. Synth. Catal. 2002, 344, 1135. (f) Medici, S.;
Gagliardo, M.; Williams, S. B.; Chase, P. A.; Gladiali, S.; Lutz, M.; Spek,
A. L.; Van Klink, G. P. M.; Van Koten, G. Helv. Chim. Acta 2005, 88, 694.
(g) Gagliardo, M.; Chase, P. A.; Lutz, M.; Spek, A. L.; Hartl, F.; Havenith, R.
W. A.; Van Klink, G. P. M.; Van Koten, G. Organometallics 2005, 24, 4553.
(h) Gagliardo, M.; Amijs, C. H. M.; Lutz, M.; Spek, A. L.; Havenith,
R. W. A.; Hartl, F.; Van Klink, G. P. M.; Van Koten, G. Inorg. Chem.
2007, 46, 11133. (i) Li, J.; Minnaard, A. J.; Klein Gebbink, R. J. M.; Van
Koten, G. Tetrahedron Lett. 2009, 50, 2232. (j) Bonnet, S.; Li, J.; Siegler,
M. A.; Von Chrzanowski, L. S.; Spek, A. L.; Van Koten, G.; Klein Gebbink,
R. J. M. Chem.;Eur. J. 2009, 15, 3340.
(7) (a) Tsang, C.-W.; Rohrick, C. A.; Saini, T. S.; Patrick, B. O.;
Gates, D. P. Organometallics 2002, 21, 1008. (b) Tsang, C.-W.; Rohrick,
C. A.; Saini, T. S.; Patrick, B. O.; Gates, D. P. Organometallics 2004, 23,
5913.

Article
Organometallics, Vol. 28, No. 20, 2009 5955
Figure 2. Computed energetic pathway for the transformation of 1 into 2 in the case of nickel. Energies are given in kcal/mol.
above, when a ligand (PCy3 with Ni(COD)2 or TOP on Ni
nanoparticles) was present, no reaction occurred. Therefore,
all our calculations were conducted assuming that no other
ligand apart from 1 is linked to nickel during the transforma-
tion. The complete computed energetic pathway is presented
in Figure 2.
Nickel can bind to ligand 1 either through the lone pair of
1 (Z1-coordination) or through the π-system (Z2-coor-
dination). Calculations revealed that the 12-VE Z1-complex
INi is less stable than the 14-VE Z2-species IINi by 23.6 kcal/
mol. Interestingly, IINi involves the Z2-coordination of a
˚
˚
C-H bond (d(Ni-H) = 1.727 A, d(Ni-C) = 2.155 A, d(C-
˚
H) = 1.138 A) of one methyl group of one the tert-butyl
Figure 3. View of the theoretical structure of IIINi-TS-IVNi.
Selected bond distances (A) and angles (deg): P-C(1) 1.786,
C(1)-C(2) 1.433, C(2)-C(3) 1.437, C(3)-Ni 2.110, C(2)-Ni
2.103, C(1)-Ni 2.029, P-Ni 2.282, H-Ni 1.502, C(4)-Ni 2.020,
C(4)-P 2.389, H-Ni-P 133.218, H-Ni-C(1) 165.872,
H-Ni-C(2) 127.200, H-Ni-C(3) 92.252, H-Ni-C(4) 89.883,
Ni-C(4)-P 61.676, C(4)-P-Ni 51.170, P-Ni-C(4) 67.154.
groups on the highly unsaturated Ni center. As expected, this
complex is the precursor of the Ni(II) hydride species IIINi,
which results from the insertion of nickel into the C-H bond
(IINi-TS-IIINi). As can be seen, this intramolecular C-H
oxidative addition is quite facile, requiring a small activation
barrier (ΔEq = þ11.1 kcal/mol). Activation of an aliphatic
C-H bond by a late transition metal, especially on the R-
position of a P-aryl group such as P(o-tol)(R)2 or P(R)2Mes,
to yield the cyclometalated product was already reported,8 as
well as other C-H bond activations on aliphatic phosphine
complexes of various transition metals.9 Complex IIINi is a
16-VE species in which both the PdC double bond and one
CdC bond of the phenyl ring are coordinated to Ni. From
this hydride complex, the next step involves the formation of
the P-C bond to yield the benzophospholane complex IVNi
through an exothermic process (ΔE=-8.9 kcal/mol). Com-
plex IVNi is a 14-VE species that features coordination of a
Z3-benzyl ligand. A view of the transition state (IIINi-
TS-IVNi) is presented in Figure 3, and the most significant
metric parameters are listed in the corresponding legend. We
then found that complex IVNi can isomerize into the 14-VE
species VNi, which involves coordination of the phosphorus
˚
atom lone pair of the benzophospholane unit. The two
complexes possess very similar energy, and the isomerization
involves here again a weak activation barrier of ΔEq= þ10.3
kcal/mol.
Finally it appears that the structure of complex VNi is
well adapted to the final reductive elimination, which affords
the 12-VE Z1-complex Ni(0) VINi. This reductive elimina-
tion process is the rate-determining step of the whole process
(ΔEq = þ14.3 kcal/mol), which is highly exothermic (from
INi to VINi ΔE = -27.6 kcal/mol). Importantly, we note
that all the energetic barriers involved in this computed
pathway are compatible with the experimental conditions
used.
Mechanism with Pt. Having proposed a mechanism for the
stoichiometric transformation involving nickel, we then
turned our attention to the platinum-catalyzed process. In
contrast to the reaction promoted by Ni(0) species described
above, monitoring the catalytic experiments by 31P NMR
revealed that a few intermediates could be observed in the
case of both the mono-phosphaalkene 1 and the bis-phos-
phaalkene 4. However, because of the catalytic loadings,
these species were observed in minor amounts, which
prompted us to carry out stoichiometric reactions in C6D6
to attempt the identification of some intermediates by
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€
C.-P.; Riermeier, T. H.; Ofele, K.; Beller, M. Chem.;Eur. J. 1997, 3, 1357.
€
(d) Hermann, W. A.; Bohm, V. P. W.; Reisinger, C.-P. J. Organomet. Chem.
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5956 Organometallics, Vol. 28, No. 20, 2009
Houdard et al.
Figure 4. Computed energetic pathway for the transformation of 1 into 2 using [Pt(PMe3)] as catalyst. Energies are given in kcal/mol.
31P{1H} and H NMR. Essentially the same intermediates
were observed in the two cases, showing that the two
phosphaalkene moieties in 4 react independently and succes-
sively and that the phosphorus atoms are not electronically
coupled. The reaction between 1 and [Pt(PCy3)2] was highly
informative, even in the early stages. Indeed, within 15 min,
the 31P NMR spectrum showed the presence of the two
starting materials (δ = 257 ppm for 1 and 62 ppm for
[Pt(PCy3)2]), but also the formation of a new complex
(roughly the same intensity as 1) and the release of 1 equiv
of PCy3 as well as the final product. This complex is
characterized by an AMX spin system pattern with two very
different JPt-P coupling constants and a relatively small
2JP-P coupling constant, attesting to a cis location of the
two phosphine groups:10 at δ = -31.0 ppm (1JPt-P = 984
Hz, 2JP-P = 27.9 Hz) and δ = þ51.7 ppm (1JPt-P = 2952
Hz, 2JP-P = 27.9 Hz). Importantly, recording of the corre-
sponding 1H NMR spectrum indicated that this intermediate
is a platinum hydrido complex (1JH-Pt = 1711 Hz) and that
the hydride ligand is located trans to the upfield shifted
phosphorus atom (2JH-P=176 Hz). This was confirmed by
the 31P spectrum, in which the signal at -31.0 ppm is further
split because of the large 2JH-P coupling constant of 176 Hz.
According to the 31P NMR spectroscopy, this stoichiometric
reaction afforded, after 2 h at room temperature, compound
2 and the catalytic precursor [Pt(PCy3)2], which has been
partly re-formed. Overall, this mechanistic study provided
the following key points for the DFT calculations: (a) 1 equiv
of PCy3 is released during the process; (b) a complex featur-
ing two types of phosphines and one hydride ligand is an
observable intermediate.
this energetic pathway is quite similar to that proposed in the
case of nickel. The first step of the mechanism involves
coordination of the phosphaalkene onto the 12-VE
[Pt(PMe3)] fragment. Contrary to the analogous nickel
species IINi, formation of the Z2-complex IIPt is slightly
exothermic. IIPt is a 14-VE complex that features only a very
weak agostic interaction with one hydrogen atom of one tert-
1
˚
˚
butyl group (d(Pt-H) = 2.220 A, d (C-H) = 1.108 A vs
˚
1.099 A for the two other C-H bonds of the methyl group).
Like in the case of nickel, formation of complex IIIPt, which
results from the insertion of the platinum fragment into the
C-H bond, is an exothermic process (ΔE = þ6.6 kcal/mol)
that requires an activation barrier of ΔEq = þ14.6 kcal/mol
(through IIPt-TS-IIIPt). Complex IIIPt is a tetracoordi-
nated 16-VE hydrido complex that adopts a distorted
square-planar geometry (CH2-Pt-H = 70.7°, H-Pt-P
(of PMe3) = 77.7°). Like in the case of nickel, the following
step is the ring closure forming the benzophospholane ring.
This step, which also requires a relatively weak activation
energy (ΔEq = þ11.4 kcal/mol through IIIPt-TS-IVPt),
was found to be much more exothermic (ΔE = -22.6 kcal/
mol) than in the case of nickel. The new complex formed,
IVPt, is a 16-VE hydrido complex that involves the Z3-
coordination of a benzylic ligand. The second part of the
mechanism is also similar to that proposed in the case of
nickel apart from the formation of the 16-VE hydrido
complex VIPt, which could not be rationalized without
considering that IVPt first undergoes decomplexation of
the arene moiety to afford the 14-VE hydrido complex VPt,
which adopts T-shaped geometry (no acceptable transition
state structure connecting IVPt to VIPt was found). Impor-
tantly, we found that VIPt lies at lower energy than the other
hydrido intermediates. Therefore one can reasonably assume
that this intermediate corresponds to the hydrido complex
observed in both the 1H and 31P NMR spectra. As expected,
the hydride ligand is located trans to the benzophospholane
ligand (the most upfield shifted phosphorus signal), the two
Calculations were thus undertaken and, in order to save
computation time, the remaining coordinated PCy3 was
modelized by a PMe3 group. The overall energetic pathway
is presented in Figure 4. From a mechanistic point of view,
(10) Cowan, R .L.; Trogler, W. C. J. Am. Chem. Soc. 1989, 111, 4750.

Article
Organometallics, Vol. 28, No. 20, 2009 5957
pendant ligands. Although no experiments have been carried
out in this direction, one may reasonably expect that this
rearrangement could also be extended to functional phospaalk-
enes featuring other aromatic substituents at the carbon atom.
Furthermore, the appreciable kinetic stability of intermediates
such as VIPt also offers interesting perspectives because of the
presence of a potentially reactive Pt-H bond. All these devel-
opments are currently underway in our laboratories and will be
reported in due course.
Experimental Section
Synthesis. All reactions were routinely performed under an inert
atmosphere of argon or nitrogen using Schlenk and glovebox
techniques and dry deoxygenated solvents. Dry hexanes and
tetrahydrofuran were obtained by distillation from Na/benzophe-
none. Dry dichloromethane was distilled on P2O5 and dry toluene
on metallic Na. Nuclear magnetic resonance spectra were recorded
on a Bruker AC-300 SY spectrometer operating at 300.0 MHz for
1H, 75.5 MHz for 13C, and 121.5 MHz for 31P. Solvent peaks are
used as internal reference relative to Me4Si for 1H and13Cchemical
shifts (ppm); 31P chemical shifts are relative to an 85% H3PO4
external reference. Coupling constants are given in hertz. The
following abbreviations are used: s, singlet; d, doublet; t, triplet; m,
multiplet; v, virtual; p, pseudo. Compounds 1 and 4 were prepared
using the Phospha-Wittig approach, which relies on the reaction of
[Mes*PdPMe3] with the corresponding aldehydes.12 Ni(COD)2,13
[Pd(COD)Cl2],14 [Pd(dba)2],15 and [Pt(PCy3)2]16 were prepared
according to reported procedures. All other reagents and chemicals
were obtained commercially and used as received. Elemental
analyses were performed by the “Service d’Analyse du CNRS”,
at Gif sur Yvette, France.
Figure 5. View of the theoretical structure of VIPt-TS-VIIPt.
Selected bond distances (A) and angles (deg): P(1)-C 1.910, C-H
1.525, H-Pt 1.640, C-Pt 2.175, P(1)-Pt 2.434, Pt-P(2) 2.233,
Pt-P(1)-C 58.630, P(1)-C-H 120.501, P(1)-C-Pt 72.802,
C-H-Pt 86.763, P(1)-Pt-H 92.294, P(1)-Pt-P(2) 136.485,
H-Pt-P(2) 130.256.
˚
phosphines being fixed in a cis arrangement. Furthermore,
another important piece of data is given by the small
1
magnitude of the J coupling constant (984 Hz) between
platinum and the benzophospholane ligand. This phenom-
enon is not totally unprecedented, and we already noted that
Z2-coordination of a λ4-phosphinine anion to the cationic
[Pt(PPh3)Cl]þ fragment resulted in a decrease of the magni-
tude of this 1JPt-P coupling constant (1JPt-P = 2793 Hz to be
compared with 1JPt-P = 4752 Hz for the PPh3 ligand).11 To
some extent, there is an analogy between the two species
since complex VIPt can also be regarded as the complexation
of a phosphinomethanide ligand (R1R1P-C(-)R3R4) to the
cationic [Pt(H)(PCy3)]þ fragment. Finally, the last step of the
transformation is the reductive elimination, which yields the
14-VE Pt(0) complex VIIPt, which adopts a linear geometry.
The activation barrier needed to promote this transforma-
tion (through VIPt-TS-VIIPt) was found to be quite similar
to that computed in the case of nickel (ΔEq = þ14.1 vs 14.3
kcal/mol). A view of the computed structure of VIPt-
TS-VIIPt is presented in Figure 5, and the most relevant
metric parameters are listed in the corresponding legend.
Finally, our calculations also revealed that complex VIIPt
reacts with released PMe3 to regenerate the [Pt(PMe3)2]
complex (not depicted in the scheme for the sake of clarity),
in good agreement with NMR observations made during the
stoichiomertic experiment. Indeed, the conversion of VIIPt
(þ PMe3) into the free benzophospholane and [Pt(PMe3)2]
was found to be exothermic (ΔE = -9.9 kcal/mol).
Synthesis of Compound 2. Phosphaalkene 1 (100 mg, 0.27
mmol) was dissolved in 30 mL of distilled and degassed hexanes
in a glovebox. Then, [Pt(PCy3)2] (41 mg, 0.05 mmol) was added,
and the resulting solution was stirred in a oilbath at 65 °C for 15 h.
After checking by 31P NMR for complete disappearance of the
starting product, the solvent was removed in vacuo. The solid
obtained was then dissolved in a minimum amount of CH2Cl2
(5 mL) and then filtered over a pad of silica gel under an inert
atmosphere in a Schlenk filter and eluted with another 150 mL of
dry CH2Cl2. Solvent was then removed invacuo. Compound 2 was
obtained as a white solid; yield 80% (80 mg). HRMS: C25H35P
calcd 366.2476 g mol-1, found 366.2488 g mol-1. Anal. Calcd
3
3
[C25H35P] (366.5): C 81.92, H 9.63. Found: C 82.17, H 9.56.
31P NMR (C6D6) δ -7.7 (s); 1H NMR (C6D6) δ 7.28 (dd, 1H,
4JP-C = 4.0 Hz, 4JH-H = 1.7 Hz, HC5), 7.00-6.87 (m, 5H, H
aromatic), 6.80 (t, 1H, 3JH-H = 7.3 Hz, Hp of C6H5), 3.00 (dd,
Conclusion
(12) See for example: (a) Le Floch, P.; Marinetti, A.; Ricard, L.;
Mathey, F. J. Am. Chem. Soc. 1990, 112, 2407. (b) Le Floch, P.; Mathey, F.
Synlett 1990, 171. (c) Shah, S.; Prostasiewicz, J. D. Chem. Commun. 1998,
1585. (d) Shah, S.; Simpson, M. C.; Smith, R. C.; Protasiewicz, J. D. J. Am.
Chem. Soc. 2001, 123, 6925. (e) Shah, S.; Prostasiewicz, J. D. Coord. Chem.
Rev. 2000, 210, 181.
In this study, we have evidenced the first example of a metal-
mediated addition of a C-H bond onto a phosphorus-carbon
double bond. Interestingly, this rearrangement was also success-
fully extended to a bis-phosphaalkene such as 4, thus yielding a
new class of pincer ligands featuring benzophospholane as
(13) Krysan, D. J.; Mackenzie, P. B. J. Org. Chem. 1990, 55, 4229.
(14) Drew, D.; Doyle, J. R. Inorg. Synth 1972, 13, 52.
(15) Rettig, M. F.; Maitlis, P. M.; Cotton, F. A.; Webb, T. R.
Inorganic Syntheses; Angelici, R. J., Ed.; John Wiley & Sons, Inc: New
York, 1990; Vol. 28, p 110.
ꢀ
(11) Moores, A.; Mezailles, N.; Ricard, L.; Jean, Y.; Le Floch, P.
Organometallics 2004, 23, 2870.
(16) Yoshida, T.; Otusuka, S. Inorg. Synth 1979, 19, 105.

5958 Organometallics, Vol. 28, No. 20, 2009
Houdard et al.
1H, 2JP-H = 6.3 Hz, 2JH-H = 13.3 Hz, CH2 benzyl group), 2.61
(dd, 1H, 2JP-H = 6.0 Hz, 2JH-H = 13.3 Hz, CH2 benzyl group),
1.60-1.52 (m, 2H, CH2 of benzophospholane), 1.40 (s, 9H, t-Bu
group grafted on C6), 1.16 (s, 3H, Me of benzophospholane),
1.08 (s, 9H, t-Bu group grafted on C4), 0.90 (s, 3H, Me
of benzophospholane); 13C{1H} NMR (C6D6) δ 158.9 (s, C2),
grafted on C6), 34.6 (m, CH2 of benzophospholane), 34.2 (s, C
of t-Bu group on C4), 33.9 (m, CH2 benzyl group), 33.0 (s, Me of
benzophospholane), 32.7 (s, Me of t-Bu group grafted on C6),
32.2 (s, Me of t-Bu group grafted on C4) 29.7 (s, Me of
benzophospholane).
Synthesis of Compound 5. Bis-phosphaalkene 4 (100 mg, 0.15
mmol) was dissolved in 30 mL of distillated and degassed
hexanes in a glovebox. Then, [Pt(PCy3)2] (23 mg, 0.03 mmol)
was added, and the resulting solution was stirred in a oil bath at
65 °C for 15 h. After checking by 31P NMR for complete
disappearance of the starting product, the solvent was removed
in vacuo. The solid obtained was dissolved in a minimum
amount of CH2Cl2 (5 mL) and then filtered over a pad of silica
gel under an inert atmosphere in a Schlenk filter and eluted with
another 150 mL of dry CH2Cl2. Solvent was removed in vacuo.
Compound 5 (a mixture of 5a and 5b) was obtained as a white
solid; yield 82% (82 mg): HRMS C44H64P2 calcd 654.4483
g mol-1, found 654.4480 g mol-1. Anal. Calcd [C44H64P2]
152.7 (d, 2JP-C = 13.8 Hz, C6), 152.4 (s, C4), 139.6 (d, 2JP-C
=
8.0 Hz, Cipso of phenyl), 136.2 (d, 2JP-C = 24.1 Hz, C1) 129.7 (d,
3JP-C = 7.5 Hz, Co of phenyl), 128.7 (s, Cm of phenyl), 126.0 (d,
5JP-C = 2.3 Hz, Cp of phenyl), 122.0 (d, 3JP-C = 4.2 Hz, C5),
119.0 (s, C3), 46.7 (d, 2JP-C = 6.9 Hz, C-C2), 38.1 (d, 1JP-C
=
24.1 Hz, CH2 benzyl group), 37.7 (d, 3JP-C = 1.7 Hz, C of t-Bu
grafted on C6), 36.4 (d, JP-C = 9.8 Hz, CH2 of benzo-
1
phospholane), 35.1 (s, C of t-Bu group grafted on C4), 34.2 (d,
3JP-C = 4.0 Hz, Me of benzophospholane), 33.8 (s, Me of
benzophospholane), 32.7 (d, 4JP-C = 8.6 Hz, Me of t-Bu group
grafted on C6), 31.6 (s, Me of t-Bu group graftetd on C4).
Synthesis of Complex 3a. Compound 2 (75.5 mg, 0.21 mmol)
was dissolved in 50 mL of distilled and degassed toluene in a
Schlenk tube. Then, [Pd(COD)Cl2] (29.4 mg, 0.10 mmol) was
added, and the resulting clear solution was stirred in a oil bath at
110 °C for 15 h. After checking the 31P NMR for complete
disappearance of the starting product, solvent was removed in
vacuo and the product extracted from the resulting solid using
2 ꢀ 50 mL of petroleum ether. The liquid phase was filtered, and
the solvent was evaporated. The product is obtained as a bright
yellow solid. Yield: 92% (86.3 mg). Anal. Calcd for [C50-
H70Cl2P2Pd] (910.4): C 65.97, H 7.75. Found: C 65.81, H 7.79.
3
3
(654.9): C 80.69, H 9.85. Found: C 80.88, H 9.79.
Diastereomer 5a: 31P{1H} NMR (C6D6) δ -7.5 (s); 1H NMR
(C6D6) δ 7.54 (m, 2H, C5-H), 7.26 (s, 1H, C7-H), 7.20 (s, 2H,
C3-H), 7.15 (s, 2H, C9-H), 7.12 (s, 1H, C10-H), 3.28 (dd, 2H,
2JH-H = 13.3 Hz, 2JP-H = 7.1 Hz, CH2 of benzyl group), 2.90
2
2
(dd, 2H, JH-H = 13.3 Hz, JP-H = 5.7 Hz, CH2 of benzyl
group), 2.2-1.8 (m, 4H, CH2 of benzophospholane) 1.67 (s,
18H, Me of t-Bu group grafted on C6), 1.48 (s, 6H, Me of
benzophospholane), 1.34 (s, 18H, Me of t-Bu group grafted on
C4), 1.20 (s, 6H,Me of benzophospholane); 13C{1H} NMR δ
157,6 (d, 2JP-C = 1.1 Hz, C2), 151.3 (d, 2JP-C = 14.4 Hz, C6),
1
meso-Diastereomer: 31P{1H} NMR (CD2Cl2) δ 29.5 (s); H
2
1
NMR δ 7.57 (m, 2H, C5-H), 7.05 (m, 6H, Ho and Hp of C6H5),
151.0 (s, C4), 138.4 (d, JP-C = 8 Hz, C8), 134.9 (d, JP-C =
6.86 (d, 4JP-H = 1.4 Hz, 2H, C3-H), 6.66 (s, 4H, Hm of phenyl),
23 Hz, C1), 129.6 (m, C7), 127.5 (s, C10), 125.8 (d, 3JP-C = 6.3
Hz, C9), 120.6 (d, 3JP-C = 4.0 Hz, C5), 117.6 (s, C3), 45.3 (d,
2
3.81 (m, 2H, CH2 benzyl group), 3.30 (dt, JH-H = 15.4 Hz,
1
2JP-H = 4.7 Hz, 2H, CH2 benzyl group), 2.68 (d, 2JH-H = 14.9
Hz, 2H, CH2 of benzophospholane), 1.83-1.78 (m, CH2 of
benzophospholane), 1.77 (s, 18H, Me of t-Bu group on C6), 1.28
(s, 18H, Me of t-Bu group on C4), 1.18 (s, 3H, Me of
benzophospholane), 0.50 (s, 3H, Me of benzophospholane);
13C{1H} NMR δ 158.5 (s, C2), 154.0 (s, C4), 151.8 (m, C6),
134.5 (m, Cipso of C6H5), 129.6 (s, Co of C6H5) 127.3 (s, Cm of
C6H5), 125.7 (s, Cp of C6H5), 123.6 (m, C5), 123.4 (m, C1), 118.2
(d,3JP-C = 4.6 Hz, C3), 43.83(s, C-C2), 37.0 (s, C of t-Bu group
grafted on C6), 34.5 (m, CH2 of benzophospholane) 34.2 (s, C of
t-Bu group on C4), 34.1 (m, CH2 of benzyl group), 33.1 (s, Me of
benzophospholane), 32.8 (s, Me of t-Bu group grafted on C6),
32.2 (s, Me of t-Bu group grafted on C4) 30.0 (s, Me of
benzophospholane).
2JP-C = 6.9 Hz, C-C2), 36.6 (d, JP-C = 12.1 Hz, CH2 of
benzophospholane), 36.3, (d, 3JP-C = 1.7 Hz, C of t-Bu group
grafted on C6), 35.0 (d, 1JP-C = 10.3 Hz, CH2 of benzyl group),
33.7 (s, C of t-Bu group grafted on C4), 32.9 (vt, 3JP-C = 4.0 Hz,
Me of benzophospholane), 32.4 (s, Me of benzophospholane),
31.4 (d, 3JP-C = 9.8 Hz, Me of t-Bu group grafted on C6), 30.3
(s, Me of t-Bu group grafted C4).
Diastereomer 5b: 31P{1H} NMR (C6D6) δ -7.6 (s); 1H NMR
(C6D6) δ 7.54 (dd, 2H, 4JP-H = 1.9 Hz, 4JH-H = 1.4 Hz, C5-H),
7.26 (s, 1H, C7-H), 7.20 (s, 2H, C3-H), 7.15 (s, 2H, C9-H), 7.12
(s, 1H, C10-H), 3.29 (dd, 2H, 2JH-H = 13.3 Hz, 2JP-H = 7.1 Hz,
CH2 benzyl), 2.90 (dd, 2H, 2JH-H = 13.3 Hz, 2JP-H = 5.7 Hz,
CH2 benzyl), 2.2-1.8 (m, 4H, CH2 of benzophospholane), 1.67
(s, 18H, Me of t-Bu group grafted on C6), 1.50 (s, 6H, Me of
benzophospholane), 1.33 (s, 18H, Me of t-Bu group grafted on
C4), 1.21 (s, 6H, Me of benzophospholane); 13C{1H} NMR δ
157,5 (d, 2JP-C = 1.1 Hz, C2), 151.3 (d, 2JP-C = 14.4 Hz, C6),
rac-Diastereoisomer: 31P{1H} NMR (CD2Cl2) δ 30.0 (s); 1H
NMR δ 7.57 (m, 2H, C5-H), 7.05 (m, 6H, Ho and Hp of C6H5),
6.83 (d, 4JP-H = 1.4 Hz, 2H, C3-H), 6.64 (s, 4H, Hm of phenyl)
2
2
1
3.86 (m, 2H, CH2 benzyl group), 3.40 (dt, JH-H = 15.4 Hz,
151.0 (s, C4), 138.4 (d, JP-C = 8 Hz, C8), 135.0 (d, JP-C =
2JP-H = 4.7 Hz, 2H, CH2 benzyl group), 2.56 (d, 2JH-H = 14.9
Hz, 2H, CH2 of benzophospholane), 1.83-1.78 (m, CH2 of
benzophospholane), 1.79 (s, 18H, Me of t-Bu group on C6), 1.25
(s, 18H, Me of t-Bu group on C4), 1.14 (s, 3H, Me of
benzophospholane), 0.42 (s, 3H, Me of benzophospholane);
13C{1H} NMR δ 158.7 (s, C2), 154.0 (s, C4), 151.8 (m, C6),
134.5 (m, Cipso of C6H5), 129.6 (s, Co of C6H5) 127.3 (s, Cm of
C6H5), 125.7 (s, Cp of C6H5), 123.6 (m, C5), 123.4 (m, C1), 118.2
(d,3JP-C = 4.6 Hz, C3), 43.78 (s, C-C2), 37.1 (s, C of t-Bu group
23 Hz, C1), 129.6 (m, C7), 127.5 (s, C10), 125.8 (d, 3JP-C = 6.3
Hz, C9), 120.7 (d, 3JP-C = 4.0 Hz, C5), 117.7 (s, C3), 45.3 (d,
2JP-C = 6.9 Hz, C-C2), 36.9 (d, JP-C = 12.1 Hz, CH2 of
1
benzophospholane), 36.3, (d, 3JP-C = 1.7 Hz, C of t-Bu group
grafted on C6), 35.5 (d, 3JP-C = 10.3 Hz, CH2 benzyl), 33.7 (s, C
of t-Bu group grafted on C4), 32.9 (vt, 3JP-C = 4.0 Hz, C-C2),
32.5 (s, Me of benzophospholane), 31.4 (d, 3JP-C = 9.8 Hz, Me
of t-Bu group grafted on C6), 30.3 (s, Me of t-Bu group grafted
on C4).

Article
Computational Details. All calculations were performed with
Organometallics, Vol. 28, No. 20, 2009 5959
X-ray Crystallography. Data were collected at 150.0(1) K on a
Nonius Kappa CCD diffractometer using a Mo KR (λ, 0.71070
A) X-ray source and a graphite monochromator. All data were
measured using phi and omega scans. Experimental details are
described in Table 1. The crystal structures were solved using
SIR 9721 and Shelxl-97.22 ORTEP drawings were made using
ORTEP III for Windows.23
the Gaussian 03W set of programs17 using the B3PW91 func-
tional.18 The 6-31G* basis set was used for all H, C, and P atoms,
and the LANL2TZ(f) basis set19 was used to describe the nickel
and the platinum atoms. For each computed structure the
minimum energy was characterized by vibration frequencies
calculations. Transition structures were localized using the
synchronous transit-guided quasi-Newton (STQN) method.20
˚
Acknowledgment. The authors thank the CNRS and
the Ecole Polytechnique for financial support of this
work. IDRIS is also acknowledged for the allowance of
computer time (project no. 090616).
(17) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.;
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Barone,V.;Mennucci,B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson,
G. A.;Nakatsuji, H.; Hada, M.; Ehara,M.; Toyota, K.; Fukuda, R.;
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H.; Klene,M.;Li,X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken,
V.; Adamo, C.;Jaramillo, J.; Gomperts, R.;Stratmann, R. E.; Yazyev,
O.;Austin, A. J.;Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.;
Morokuma,K.;Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski,
V. G.; Dapprich,S.; Daniels, A. D.;Strain, M. C.; Farkas, O.; Malick,
D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.;
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G.; Liashenko, A.;Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.;
Keith, T.; Al-Laham,M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe,
M.; Gill, P. M. W.;Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.;
Pople, J. A. Gaussian 03, revision C.02; Gaussian, Inc.: Wallingford, CT,
2004.
Supporting Information Available: Crystal data and structure
refinement details, atomic coordinates and equivalent isotropic
displacement parameters, a complete list of bond lengths and
bond angles, anisotropic displacement parameters, hydrogen
coordinates, and equivalent isotropic displacement parameters
for complex 3a. Computed Cartesian coordinates, the three
lower frequencies, and energies of all theoretical structures. This
material is available free of charge via the Internet at http://
pubs.acs.org.
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